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SubjectRe: [PATCH] virt: vbox: fix memory leak in hgcm_call_preprocess_linaddr
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Hi,

On 28-09-2019 01:04, Navid Emamdoost wrote:
> In hgcm_call_preprocess_linaddr memory is allocated for bounce_buf but
> is not released if copy_form_user fails. The release is added.
>
> Fixes: 579db9d45cb4 ("virt: Add vboxguest VMMDEV communication code")
>
> Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>

Thank you for catching this, I agree this is a bug, but I think we
can fix it in a cleaner way (see below).

> ---
> drivers/virt/vboxguest/vboxguest_utils.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virt/vboxguest/vboxguest_utils.c b/drivers/virt/vboxguest/vboxguest_utils.c
> index 75fd140b02ff..7965885a50fa 100644
> --- a/drivers/virt/vboxguest/vboxguest_utils.c
> +++ b/drivers/virt/vboxguest/vboxguest_utils.c
> @@ -222,8 +222,10 @@ static int hgcm_call_preprocess_linaddr(
>
> if (copy_in) {
> ret = copy_from_user(bounce_buf, (void __user *)buf, len);
> - if (ret)
> + if (ret) {
> + kvfree(bounce_buf);
> return -EFAULT;
> + }
> } else {
> memset(bounce_buf, 0, len);
> }
>

First let me quote some more of the function, pre leak fix, for context:

bounce_buf = kvmalloc(len, GFP_KERNEL);
if (!bounce_buf)
return -ENOMEM;

if (copy_in) {
ret = copy_from_user(bounce_buf, (void __user *)buf, len);
if (ret)
return -EFAULT;
} else {
memset(bounce_buf, 0, len);
}

*bounce_buf_ret = bounce_buf;

This function gets called repeatedly by hgcm_call_preprocess(), and the
caller of hgcm_call_preprocess() already takes care of freeing the
bounce bufs both on a (later) error and on success:

ret = hgcm_call_preprocess(parms, parm_count, &bounce_bufs, &size);
if (ret) {
/* Even on error bounce bufs may still have been allocated */
goto free_bounce_bufs;
}

...

free_bounce_bufs:
if (bounce_bufs) {
for (i = 0; i < parm_count; i++)
kvfree(bounce_bufs[i]);
kfree(bounce_bufs);
}

So we are already taking care of freeing bounce-bufs allocated for previous
parameters to the call (which me must do anyways), so a cleaner fix would
be to store the allocated bounce_buf in the bounce_bufs array before
doing the copy_from_user, then if copy_from_user fails it will be cleaned
up by the code at the free_bounce_bufs label.

IOW I believe it is better to fix this by changing the part of
hgcm_call_preprocess_linaddr I quoted to:

bounce_buf = kvmalloc(len, GFP_KERNEL);
if (!bounce_buf)
return -ENOMEM;

*bounce_buf_ret = bounce_buf;

if (copy_in) {
ret = copy_from_user(bounce_buf, (void __user *)buf, len);
if (ret)
return -EFAULT;
} else {
memset(bounce_buf, 0, len);
}

This should also fix the leak in IMHO is a clear way of doing so.

Regards,

Hans





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